The invention is directed to a method for filtering signals, whereby signal amplitudes can be allocated to a quantized, two-dimensional reference plane, and whereby a filtered signal can be added to an unfiltered input signal for the amplification of a useful signal part after constant parts as well as high-frequency parts have been filtered out.
Over and above this, the invention is directed to an apparatus for filtering signals, whereby signal amplitudes can be allocated to a quantized, two-dimensional reference plane, and whereby a separating filter that branches the input signal as well as a frequency-dependent filter arranged in a filter branch are provided.
Such devices are particularly employed in electronic imaging processing apparatus in order to improve the image quality of images. Such image graduations particularly occur in the field of digital image processing and are improved with respect to their confidence capability with the assistance of the filter means. For example, EP-B-0 051 068 discloses a filter means of the prior art. It turns out, however, that the known filtering methods and filter devices do not supply satisfactory results particularly when the amplitude of the useful signal is not clearly higher than the amplitude of superimposed disturbances. The result of this is that signals having a low signal-to-noise ratio can only be inadequately filtered. Given, for example, image signals that are only weakly formed, such as comparatively regular textures on a surface, then, even given comparatively slight disturbances, it is not possible with the traditional methods to undertake an adequately sharp demarcation of the contours that limit the texture elements.